The Volume Use Duration directive defines the time period that the Volume can be written beginning from the time of first data write to the Volume. If the time-period specified is zero (the default), the Volume can be written indefinitely. Otherwise, the next time a job runs that wants to access this Volume, and the time period from the first write to the volume (the first Job written) exceeds the time-period-specification, the Volume will be marked Used, which means that no more Jobs can be
appended to the Volume, but it may be recycled if recycling is enabled. Once the Volume is recycled, it will be available for use again.

You might use this directive, for example, if you have a Volume used for Incremental backups, and Volumes used for Weekly Full backups. Once the Full backup is done, you will want to use a different Incremental Volume. This can be accomplished by setting the Volume Use Duration for the Incremental Volume to six days. I.e. it will be used for the 6 days following a Full save, then a different Incremental volume will be used. Be careful about setting the duration to short periods such as 23 hours,
or you might experience problems of Susan waiting for a tape over the weekend only to complete the backups Monday morning when an operator mounts a new tape.

Please note that the value defined by this directive in the susan-dir.conf file is the default value used when a Volume is created. Once the volume is created, changing the value in the susan-dir.conf file will not change what is stored for the Volume. To change the value for an existing Volume you must use the :ref:` update volume <UpdateCommand>` command in the Console.

